Warning circuits for road vehicles

ABSTRACT

In a warning circuit for a road vehicle for giving an indication to a driver if he attempts to leave the vehicle without removing the ignition key, one terminal of the vehicle battery is grounded and the other battery terminal is connected to ground through a warning device and a first grounded switch which is closed when the driver&#39;&#39;s door is opened. A second grounded switch is connected to the live battery terminal and is closed when the ignition key is in position, and means is provided for short circuiting the warning device when the first switch closes unless the second switch is still closed.

llfit'e States atem Holt Feb. 29, 1972 54] WARNING cmctms FOR ROAD 591Refereuoesqted VEHICLES UNITED STATES PATENTS [72] inventor: WilliamDavid Holt, Colne, England 3,256,461 6/1966 Foreman et al ..340/52 D[73] Assignee: Joseph Lucas (Industries) Limited, Bir- Primary ExaminerA|vin Waring mmgham, England Attorney-Holman & Stern [22] Filed: Apr.29, 1970 [57] ABSTRACT PP 2,

In a wammg circuit for a road vehicle for givlng an indication to adriver if he attempts to leave the vehicle without removing [30] ForeignApplication Priority Data the ignition key, one terminal of the vehiclebattery is grounded and the other battery terminal is connected to June9, i969 Great Britain ..29,035/69 ground through a warning device and afirst grounded switch which is closed when the drivers door is opened. Asecond [2?] CCll. grounded switch is connected to the live batteryterminal and E 5 n q is closed when the ignition key is in position, andmeans is pro- Field of Search ..340/52, 52 D, 53; 307/10 vided for shortcircuiting the warning device when the first switch closes unless thesecond switch is still closed.

l lQ FEFLLPEYY EElBP' PATENTEDFE NW 3,646,511

INVENTOR WZZn/n David M,

WA WMQWM ,IM

AfiORNEYS WARNING CIRCUITS FOR ROAD VEHICLES This invention relates towarning circuits for road vehicles for giving an indication to a driverif he attempts to leave the vehicle without removing the ignition key.

A circuit according to the invention comprises in combination first andsecond terminals between which in use the vehicle battery is connected,the second terminal being earthed, a

first earthed switch which is closed when the drivers door is opened, awarning device through which said first switch is connected to the firstterminal, a second earthed switch which is connected to the firstterminal and which is closed when the ignition key is in position, andmeans for short circuiting said warning device when the first switchcloses if the second switch is still closed.

The accompanying drawing is a circuit diagram illustrating one exampleofthe invention.

Referring to the drawing, the vehicle includes a battery 11 having itsnegative terminal earthed. The positive terminal of the battery isconnected to one side of a courtesy light 12, the other side of which isearthed through three parallel paths containing respectively a switch13, a switch 14 and a diode 15 and switch 16 in series. The switch 13 isoperated by the passenger's door of the vehicle and closes when the dooris open, the switch 14 is a manually operable switch within the vehicle,and the switch 16 is operated by the drivers door and closes when thedrivers door is opened. Closure of any one of the switches 13, 14, 16energizes the courtesy light 12.

The live side of the switch 16 is connected to the positive batteryterminal through a buzzer l7 and a resistor 18 in series, and connectedacross the buzzer is the collector-emitter path of an NPN-transistor 19,the base of which is connected to the positive battery terminal througha resistor 21 and to earth through a switch 22. The switch 22 isoperated by the ignition key of the vehicle, and closes when theignition key is in position.

When the vehicle is being driven, the switch 22 will be closed andcurrent will flow in the resistor 21, but no current will flow in thebuzzer 17 or the transistor 19. When the driver stops the vehicle, heshould remove the ignition key so that the switch 22 opens. When thedrivers door is opened, the switch 16 closes, and the transistor 19 isturned on by current flow through the resistor 21, so short circuitingthe buzzer 17. However, if the driver forgets to remove the ignitionkey, thenthe switch 22 stays closed and no base current is supplied tothe transistor 19 when the switch 16 closes. In these circumstances acircuit is completed by way of the resistor 18 and buzzer 17 to give awarning to the driver.

The purpose of the diode 15 is to prevent the buzzer 17 from beingoperated when one of the switches l3, 14 is closed.

The arrangement described has the advantage that all the switches l3,l4, l6 and 22 can be earth return switches.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent is:

l. A warning circuit for road vehicles for giving an indication to adriver if he attempts to leave the vehicle without removing the ignitionkey, comprising in combination first and second terminals between whichin use the vehicle battery is connected, the second terminal beingearthed, a first earthed switch which is closed when the drivers door isopened, a warning device through which said first switch is connected tothe first terminal, a second earthed switch which is connected to thefirst terminal and which is closed when the ignition key is in position,and means for short circuiting said warning device when the first switchcloses unless the second switch is still closed,

2. A circuit as claimed in claim 1 in which the second earthed switch isconnected to the first terminal through a resistor, and said shortcircuiting means is a transistor having its collector-emitter pathconnected across the warning device, and its base connected to thejunction of the resistor and second earthed switch. I

-3. A circuit as claimed in claim 1 or claim 2 including a third earthedswitch connected to the first terminal through a courtesy lamp, thethird earthed switch being closed when a door other than the driversdoor is opened, and a diode coupling the junction of the warning deviceand first switch to the junction of the courtesy lamp and third switch.

1. A warning circuit for road vehicles for giving an indication to adriver if he attempts to leave the vehicle without removing the ignitionkey, comprising in combination first and second terminals between whichin use the vehicle battery is connected, the second terminal beingearthed, a first earthed switch which is closed when the driver''s dooris opened, a warning device through which said first switch is connectedto the first terminal, a second earthed switch which is connected to thefirst terminal and which is closed when the ignition key is in position,and means for short circuiting said warning device when the first switchcloses unless the second switch is still closed.
 2. A circuit as claimedin claim 1 in which the second earthed switch is connected to the firstterminal through a resistor, and said short circuiting means is atransistor having its collector-emitter path connected across thewarning device, and its base connected to the junction of the resistorand second earthed switch.
 3. A circuit as claimed in claim 1 or claim 2including a third earthed switch connected to the first terminal througha courtesy lamp, the third earthed switch being closed when a door otherthan the driver''s door is opened, and a diode coupling the junction ofthe warning device and first switch to the junction of the courtesy lampand third switch.